Internal combustion engines with port fuel injection and direct fuel injection (PFI-DI) have many advantages, such as emission performance and engine optimization. At low loads, the use of port fuel injection reduces engine emission, improves fuel vaporization, and reduces pumping losses and fuel consumptions. At high loads, the use of direct fuel injection increases combustion efficiency, improves engine performance, and fuel consumption. Direct fuel injection is also utilized during cold-starts to improve catalyst warm up time. However, operation of the direct injection system produces noises, such as ticking, and under certain operating conditions are noticeable to the occupants of the vehicle, which may cause them concern and/or dissatisfaction.
One approach to mitigate noises produced by operation of the direct injection system is shown by Krengel et al in U.S. Pat. No. 7,373,924. Therein, noise is mitigated by controlling the solenoid valve of the high pressure pump. Specifically, the solenoid valve is disabled under engine operating conditions when the engine noise and the noise, vibration, and harshness (NVH) hardware is not adequate to mitigate the direct injection system noise, such as during engine cold-starts and warm idle conditions. Another example approach to mitigate noises produced by the direct injection system shown by Mueller et al in U.S. Pat. No. 8,161,945 consists of placing an in-line noise filtering device in the direct injection system to reduce the NVH of the system.
However, the inventors have identified potential issues with the above solutions. In the approach of Krengel, direct injection usage is limited. Specifically, by disabling the solenoid valve of the high pressure pump during conditions when the noise from the direct injection system may be heard by the occupants of the vehicle, direct injection cannot be fully utilized to improve overall engine and emission efficiency. In the approach of Mueller, additional NVH hardware, such as an in-line noise filter, takes up more space and increases costs.
The inventors have recognized the above mentioned issues and developed a method for mitigating the noise of the direct injection system. The method comprises, during a first engine start, operating the engine at a first, higher, idle speed while performing direct fuel injection and during a second engine cold-start, operating at a second, lower, idle speed while performing only port fuel injection. Further, during a warmed up idle speed and in response to a direct injector cleanout cycle, with an engine temperature below a temperature at which the cooling fan is activated, activating the cooling fan while performing a cleanout cycle. In this way, the engine may be run more efficiently for combustion and emission by allowing the use of port fuel injection and direct injection under all operating conditions while mitigating the noise of the direct injection system during certain operating conditions.
As an example, a system at a warm idle may need to perform a direct injector cleanout cycle to remove coking on the injector tips. During a warm idle, the engine speed is low and the engine temperature is below a threshold at which the engine cooling fan is run. The noise from the direct injection system may be heard by the vehicle occupants and cause them concern during the cleanout cycle. To mitigate the noise, the engine cooling fan may be turned on at an overlapping period with the direct injection cleanout cycle. The engine cooling fan is a noise occupants are familiar with and operation of the engine cooling fan during a warm idle reduces the noise level of the direct injection system.
In this way, an engine component already present may be advantageously used during selected conditions to mitigate the noise of the direct injection system. By operating the engine cooling fan or changing the engine idle speed, a familiar engine noise is provided which mitigates the direct injection system noise. For example, the engine idle speed may be increased during an engine cold-start when the direct injection is run to improve catalyst warm up time to mitigate direct injection noise. The use of the engine cooling fan or changing the engine idle speed allows for a reduction in NVH hardware, reducing cost of the direct injection system, and allows for the port fuel injection and direct injection (PFI-DI) engine to be run more efficiently.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.